The present invention pertains to pressurized aircraft fuselages and, more particularly, a method for monitoring of such fuselages to detect deterioration of the pressurized compartments of the aircraft by measuring leakage of the pressurizing air therefrom and to apparatus for effecting the method.
Recent aircraft accidents involving catastrophic failure of portions of the aircraft fuselage have focused attention on the need for monitoring systems for detecting component deterioration and/or improper operation of the closure systems which may lead to such failures. The aircraft fuselage consists of a grid of bulkheads and stringers fabricated of aluminum alloy and a covering of alclad sheet rivetted to the bulkheads and stringers and forming the aerodynamic surface of the plane. While alclad sheet is formulated to be highly resistant to corrosion, consisting of high strength aluminum alloy, clad (usually on both surfaces) with a slightly different alloy, usually commercially pure aluminum, chosen for high resistance to corrosion, localized corrosion does occur over time, particularly at rivetted joints. As such corrosion is predominately in the high strength alloy rather than the cladding, it is not readily detectable until significant deterioration has occurred.
Aircraft having pressurization systems, which constitute the majority of aircraft in commercial operation, are particularly susceptable to such accidents. This is a consequence of the repeated cycles of stress imposed on the aircraft structure by the pressurization and depressurization sequence which occurs on each flight of the aircraft. The resultant cyclic loading of the fuselage structure, together with corrosion, causes gradual degradation of the fuselage. This synergistic effect of corrosion and cyclic stress is well recognized in the industry. These effects result in the gradual development of looseness around the rivets and cracking between rivets.